Recapped the Avanti and....
 

Well the recap went well. I had to readjust the contrast, vertical size and a few other adjustments. A few of the caps were 50% or more out of tolerance. I changed the 10uf 350V in hopes it would get rid of the jail bars (picture attached), but it didn't. They're pretty faint, but noticeable in dark scenes. Is there another area I should be looking to fix?

I also changed the subcarrier regenerator module as the current one wouldn't adjust the APC correctly (the pot had a messed up slot for the driver and the center leg was loose in the circuit board hole). I was unable to get the pot to turn correctly. By the damage to the face and the leg, it looks like someone put too much pressure on it, stripped it and pulled the leg out.

I started the convergence from scratch and after an hour or so, I got most of the screen converged (picture attached). The only part is the top center. I tried so hard to get it converged, but it wasn't meant to be. I can live with this over how it was.

Call me crazy, but those jailbars look just like my samsung when i tried a faulty out of spec flyback on it, until i replaced it with a higher quality flyback.

I'm assuming the flyback is part of the tripler? If so, it seems to be the original unit in the TV. For the most part, it's quiet and there's no smell. Beyond those two things, I have no idea how to figure out if it's working or up to specs. :(

The flyback supplies the input signal to the tripler and is not part of it.
This could be an issue with the horizontal drive or the tuned circuits around the HOT, flyback, yoke or damper system.

I'm attaching a pic of the high voltage area. I see the tripler, but the other pieces are unknown to me. The SM doesn't go into detail about what things look like and they don't provide pics. The multi-wire plug on the side must be feeding the tripler, so if I trace it back I'll find the flyback?

Thanks

The fly is the black thing with the red wire coming out the top with the black goo. The multi wire plug feeds the flyback

The Tripler is the gray square thing top right. I don't think it could cause jail bars but maybe someone else would know.

Did you just replace the Electrolytics? I know it uses modern film caps but they are still pushing 40 years old, I'd replace any in the Horiz sweep section just to be safe.

Sometimes RF modulators can cause this also

That's gonna be a tough one. They list electrolytic separately, but all others are lumped together without noting what kind.

I thought about that, so I connected a VCR directly to the set and the same appears in dark scenes.

'taint the flyback - most likely a filter cap in the B+, particularly the cap(s) feeding the horizontal driver/output and boost filter. Those Zenith flys usually arced internally when they fail, causing snivets and tearing in the picture.

What signal source are you using? RF Modulators in VCRs can cause this, as well as your humble cross-hatch generator.

I've also seen bad IF cables cause jailbars - usually the result of someone jerking too hard when removing them. Really bad on lowband VHF, which is what we use with most modulated signals now (Channels 3 or 4). It could be an IF cable isn't plugged in all the way , leaving a ground loop.

Check the caps first, then the IF Cables.


Cheers,

Does the Avanti have direct video in? If not, then your are connecting through an RF modulator in the VCR, right?

Cheers,

Would the caps for the B+ be in the large canister? I've changed all other electrolytic caps except for the canister. I can't find a replacement and the replacement 400uf caps are 23 dollars each and requires two of them. The two 500uf caps are cheaper.

I was using the RF in the VCR as well as an RCA external modulator for my DVD and Roku players. The effect is still there no matter which one I use. I'll open the back tomorrow and check the IF lead.

You dont have to buy the same type can caps. Use individual ones under the chassis or restuff the cans. What voltage are those caps?

If those can caps (twistlocks, FPs, TVLs, can caps) are 450V or less, common 450V types are cheaper, and you dont' even have to restuff them, just isolate them and add the caps under the chassis. Radial 450V caps are cheaper (most less than 2 bucks each) than axial caps at Mouser. I've also used 450V Panasonic caps I got from Talon. JustRadios in Canada has them too in generics - both axial and radial types.

Doug's (DRH4683) capacitor restuff tutorial here on the forum is great if you choose to restuff the originals.

Cheers,

the large oval shaped cap is part of the power supply voltage regulation system. if its not hot its OK. Its an oil filled 3.5uf cap, generally used for motor start caps on large AC motors. If the circuit breaker is not kicking out its prob ok.

50% out is not a problem with most eletrolytic caps of that era, I doubt that is causing the issue.

Older zeniths with jail bars would point towards blanking diodes in the video circuit. I would have to look at the schematic to see how blanking is accomplished here.

there is indeed a horz blanking diode and transistor that takes a pulse from the flyback to blank the video. You should scope there to see the blanking pulse check for correct amplitude, if incorrect then you could look for some componet (diode transistor resistor, there is not much too it).

The canister contains two 400uf 150V and two 500uf 35V caps. The cheapest 400uf I can find is a 200V for 23.89 on Mouser. That is for an axial. All other types are either too large or even more expensive. The 500ufs are much cheaper. So even if I wanted to rebuild the cap network on the bottom side of the board, I'm still looking at over 60.00 for a few caps.

As for checking the blanking pulse, would I use a scope for that? My brother has one and I'm sure I can get him to bring it over.

radials are much cheaper why are you replacing them anyway? are they bad?

I'm not replacing them (yet, if at all). I replaced all the exposed electrolytic caps based on age. I'm now tracking down the jail bar issue and someone mentioned the B+ voltage and a possible cap problem. Since I replaced all other caps, I asked if the B+ cap was inside the canister, if not I've already replaced it. If it is in the canister, I'd have to remove it, test it and replace if necessary.

I cannot find a radial cap that's 400uf 150V. I only find an axial 400uf 200V and I'm not giving them 23.89 for it. :nono:

...

Okay, so a 470uf 20% wouldn't put it outside of the intended operating range? A 400 at 20% could be as low as 320 and as high as 480. The 470 could be as high as 517.

I'm not too up on tolerances and when it matter most/least.

the orig caps were prob -50% to +100% on the can caps.

generally speaking you can go up to the next common value.

The 2 400mfd caps are in the 125 scorce. Take a cap 100-200mfd
200V or more & hang it in parallel with the 400mfd section with
clip leads. Turn set on & see if it cures it. Do the same with
the other 400mfd.
The 500 is in the 24V. Do the same thing but BE SURE
you discharge the subbing cap first.

One other thing is lead dress be sure nothing like the yoke
wires are near the CRT harness.

Also looks like there is still an old 22-5001 cap on the flyback
board, change it !

73 Zeno:smoke:

That pic is before the recap. All the safety caps have been changed to the orange drops (4 of them).

I think I have some caps to put in parallel. If not, my brother should. I'll let you know what happens.

As for the discharging, would leaving the set unplugged for a day do that? If not, which is the cap I should discharge? I think I have a high wattage ceramic resistor I could use.

I'm attaching a pic of the internals. I'm assuming the harnesses are in their factory positions, but if you notice something amiss, let me know.

Thanks

OK on cap, I tend to notice those things.

Discharge the cap that you use to sub. If you dont it can be charged
up to 125V when you move it to the 24V & bad things can happen.
In the all tube days we would just ground the neg of the
cap & touch the sections one at a time. Anything solid state
we would hang it in, turn on, see results. Then discharge
& do the next section. Gotta be more careful, transistors
are not forgiving like tubes.

BTW its good you had to readjust after the recap. It shows
you did have bad caps.

If you still have the jail bars after above I have the Sams out & me
& the other cats will try to help you along.....

73 Zeno:smoke::beer:

Okay, hang in here with me. I just want to make sure this is as simple as I believe it is. I will take a clip-on lead from the ground point of the canister and then a clip-on lead from one of the 400uf legs of the canister. I will then take the other ends of the leads and clip them to a good cap and turn the set on. Is this correct? Also, if I'm reading the schematics correctly, the second 400uf cap is on the other side of the 16ohm filter that the first 400uf connects to. Should I do parallel both at the same time?

Okay, did some digging and found a couple 300uf 150V -10/+100% caps that measure out to roughly 415uf each. So it looks like I'm in good shape to test. Now all I need is confirmation if I should parallel both of the 400uf caps in the canister independently, or simultaneously.

Negative to ground + to the can section. OK ?
The 16 ohm is a choke, common arangement called a pi filter.
Do one cap at a time. Sometimes subbing either side will
improve it, the bad part is the one that shows most improvement.


73 Zeno:smoke:

Oh yeah, should I put the caps on single or should I series them? If I put one on, it will be a 400uf in parallel with what ever value the can still has. If I series them first, then it will add around 200uf to what ever value the can has left.

Thanks

The old caps should be disconnected completely, besides adding capacitance they can still short out if left in the circuit, and they can also be leaky between sections.

Some of us like to gut the old cap and put the new ones inside for appearances sake.

At this point I'm just trying to see if the jail bars change based on the addition of the paralleled cap. If it's best to disconnect the lead from the canister, then I think I'll just get all the replacement caps needed to clone the canister, install them on the bottom side of the chassis and leave the can in place for show.

100% correct but we are just doing a quick test to see if the
jail bars go away. Dont unhook the old ones. Since the old
caps are probably near OK otherwise you would have servere
symtoms. We always used a 80 or 100mfd for this test.
Whatever was laying on the bench.
Even if you had a totally open say 200mfd it would make a
huge improvement & you could check the set for other problems
before giving an est.

73 Zeno:smoke:

Well I paralleled both of the 400uf caps with a 200uf and it had no affect on the jail bars. Now I did those separate of each other as I don't have enough caps to do both at the same time. Should I get another 200uf cap and do both at the same time, or is it time to look elsewhere for the problem?

I didn't do anything with the 500uf caps as those are for the 24V.

...

my chromamcolor II had jailbars too.only on dvd.on satellite,no jailbars.i use an rf converter to operate multiple sets and when i disconnect 5 of the 6,jailbars disappear!

If it is source-dependent, there are likely variations in programme luminance content. Sometimes a DVD will flaunt the monitors' tiny errors.
For example, a strong signal with minimal attenuation in the highest of video frequencies(minimal sharpness) will tend to look the best, but wil usually be the most crucifyingly transparent when it comes to any defects.
On a set with power supply issues, in the form of either poor filtering on the supply rails or noise entering the video after the IF strip, It will never perform as new until the issue is eliminated.
Case in point, a 1981 zenith 19" with 9-160 mainobard and direct-entry tuner, hard power switch/vol. I used to use.

when you get done with all that, don't forget to check the horz blanking circuit.